For a conventional portable electronic device, if it is desired to be used at anytime and anywhere, it will need to consume the power of a battery installed in the portable electronic device. When the power becomes insufficient, other external power sources are needed. However, when the consumer uses the conventional portable electronic device, especially the notebook computer, a frequently encountered problem is that the battery of the notebook computer is exhausted, and the notebook computer needs to connect to other external power source or replace the battery with a new one. This not only causes trouble to the user, but also reduces the convenience in using the notebook computer.
After some manufacturers carefully researched the reasons that contribute to the power insufficiency, it has been found that one major reason is when the notebook computer is powered off, the battery of the notebook computer still supplies power to logic circuits located in the notebook computer, for example, a South Bridge chip, a keyboard controller (KBC) and the like, such that the notebook computer still consumes approximately 100 to 150 mW of power when it is powered off. Furthermore, if voltage of I/O pins located in the notebook computer is not set at correct level, the power consumption will be higher, which will even cause electric leakage of IC. As such, even through the notebook computer is not used, the power will still be exhausted after a period of time, which not only wastes the power, but is also a nuisance the user often complained about.